Power control is an important functionality in a mobile communication system. Power control may be used for saving terminal or base station power consumption and/or to ensure coverage by the mobile communication system and sufficient capacity. With increasing popularity of mobile voice and data communication, there is an ever increasing demand for efficient power control to increase system capacity.
Techniques for downlink power control are generally resident in a mobile communication terminal. The downlink power control techniques may also include components in the mobile communication network, e.g. in the radio access network. For illustration, an open loop power control may be used in a base station to estimate an initial output power for downlink transmissions when a new connection is established.
One or several power control algorithms may be used in the mobile communication terminal. For illustration, in Wideband Code Division Multiple Access (WCDMA) networks, an outer loop power control and an inner loop power control may be implemented in the mobile communication terminal for downlink power control.
The outer loop power control for the downlink, which is also referred to as downlink outer loop power control herein, is an algorithm for maintaining an acceptable target signal-to-interference ratio (SIR). In order to define a certain target SIR target, the downlink outer loop power control algorithm conventionally estimates a packet block error rate (BLER) from base station transmissions.
The downlink inner loop power control, which is also referred to as closed loop power control or as fast inner or closed loop power control, is responsible for following the specific target SIR defined by the downlink outer loop power control. The downlink inner loop power control for downlink transmissions resides in the mobile communication terminal and sends explicit power up or power down commands to the base station.
The determination of the BLER required for the downlink outer loop power control may be a comparatively slow process, in particular when the BLER is low. The determination of the BLER then requires incoming packets to be monitored for a BLER for an extended time to obtain a reliable estimate for the BLER. This process, also called convergence of the BLER determination or convergence of the downlink outer loop power control, may have the effect that the base station continues to transmit signals with powers that are greater than would actually be required, because the downlink outer loop power control resident in the mobile communication terminal is still in the convergence phase. This may increase interference also for other mobile communication terminals. Increased power consumption and/or lower system capacity may result.